Like their cephalopod cousins the octopuses, cuttlefish are masters of disguise.
As they hunt, these marine predators send waves of color across their skin. The rainbow display freezes prey in place, granting the cuttlefish just enough time to shoot out two specialized hunting tentacles at lightning speed and snatch them into range of their deadly beaks.
But can cuttlefish actually mesmerize prey with their colorful skin changes? Or is something more complex at play?
Experts say cuttlefish are ingenious hunters, but the mechanism at work on the seafloor is likely more mysterious than simple hypnosis.
A Calculated Hunter
Cuttlefish are visual hunters, using their large, complex eyes to locate and track potential meals. Their strategy generally involves a slow, stealthy approach, said Bret Grasse, manager of cephalopod operations at the Marine Biological Laboratory in Woods Hole, Massachusetts.
“The cuttlefish will slowly approach the prey so as not to alert the unsuspecting shrimp, fish, or crab,” Grasse explained.
During this approach, cuttlefish often put on a showy display, producing moving bands of color across their bodies. These displays are generated by a combination of light-reflecting pigment cells—iridophores, leucophores, and chromatophores—which contract and expand to produce specific colors and patterns within milliseconds.
While some may wonder if this display mesmerizes prey, scientists don’t think that’s the case. Hypnosis, defined as a mental state of increased relaxation and altered awareness, is considered a uniquely human psychological state. There is very little research on whether fish can be hypnotized; a 2005 study found that a steady stream of water could induce an immobile state in snapper (Chrysophrys auratus) similar to hypnosis, and other research has shown zebrafish possess molecular receptors for sedative hypnotic drugs. However, whether fish can be visually induced into a hypnotic state has not been directly studied.
Although some animals, such as chickens, can be induced into trance-like conditions of tonic immobility—an involuntary, temporary state of unresponsiveness triggered by extreme trauma—it is unlikely that the cuttlefish’s color changes “hypnotize” their prey, said Connor Gibbons, cephalopod facility manager at Columbia University. Instead, researchers believe the color show serves as an ingenious disguise.
As waves of different colors ripple down the cuttlefish’s body, the animal’s outline becomes less distinct to its prey, so they may not recognize the cuttlefish as a threat, Gibbons said.
“It’s only part of something looming at them, which they’re like, ‘I don’t know if you are a predator? Are you just passing waves? What are you?'” Gibbons said. “And then by that time, it’s too late.”
Once they get close enough, the cuttlefish shoots its two long, specialized feeding tentacles from small hidden pouches near the mouth at the prey.
“The closest thing I can compare it to is the tongue of a chameleon extending out to grab an unsuspecting insect,” Grasse said. “Cuttlefish feeding tentacles fire out in the blink of an eye before the prey can react and escape.”
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Then, the prey is pulled toward the cuttlefish’s mouth, pierced by its sharp, chitinous beak, and injected with venom. The venom helps the cuttlefish reduce energy usage during hunting, “as the cuttlefish does not want to use unnecessary energy and struggle against the prey while it’s trying to eat,” Grasse said.
However, the notion that cuttlefish flash colors to hide their body shape is only one hypothesis for these strobing displays. Other researchers, including Grasse, describe them as a way to distract prey.
“Essentially, they are trying their best not to alarm the prey to their presence,” he said. By breaking up the outline of their bodies, cuttlefish can convince prey they are not as large or threatening as they appear.
Whether the light shows function primarily as disguise or distraction remains unresolved, Gibbons said, and scientists also need a better understanding of how the cuttlefish controls its deadly dermal display. “The jury is still out on exactly what is happening,” he said.